It is estimated that in the United States alone, over 1.5 billion tons of animal waste are produced annually. While a portion of this waste is generated on farms where disposal may consist of on-site manure spreading, large amounts are also produced in feedlots, many of which are located near urban areas. For a number of reasons, manure spreading, incineration and other traditional waste disposal alternatives may be undesirable or impractical. Hence, economical animal waste processing methods which produce environmentally desirable products are needed.
Modern animal feedstuffs are complex mixtures of protein, fiber, vitamins, minerals, salts and other components, balanced to provide optimum nutrition at minimum cost. Sodium, calcium, phosphorous, magnesium, potassium, and other minerals are present in most feedstuffs. In addition, large amounts of chlorides are ingested by livestock, often from salt-blocks and the like. The ingestion of salt is known to increase the thirst and appetite of animals which increases body weight. Although nutrient-enriched diets are designed to produce healthier, more marketable likestock, the high concentrations of chlorides, ammonia, and minerals which these highly nutritious feedstuffs produce in animal waste are of particular concern in waste processing systems.
Generally, livestock waste contains from about 8 percent to about 11 percent by weight carbonaceous material, although concentrations outside this range are not uncommon, depending on the amount of wash-down water present. Unprocessed or raw animal wastes typically have a chemical oxygen demand (COD) of from about 80,000 mg/l to about 120,000 mg/l. The chemical oxygen demand is a measure of the quantity of chemically oxidizable components present in the waste. Animal wastes also generally have a biochemical oxygen demand (BOD) of from about 40,000 gm/l to about 90,000 mg/l. The biochemical oxygen demand is the quantity of oxygen required during decomposition of the organic waste matter by aerobic biochemical action. The BOD is usually determined by measuring oxygen consumption of decay microorganisms in a waste sample during a five-day period at 20.degree. C. As will be appreciated by those skilled in the art, one important objective of waste treatment processing is the reduction of the oxygen demand of the waste effluent. Oxygen depletion or deoxygenation of receiving waters due to the discharge of waste effluents having high oxygen demands is a significant environmental concern and is the subject of considerable governmental regulation.
Waste processing systems are designed to provide the most environmentally compatible waste effluent at the lowest cost, with maximum utilization of process by-products. Thus, processing schemes which require a relatively low initial capital expenditure and which have low operational and maintenance costs are highly desirable. Those conventional waste processing systems which are adaptable to processing animal wastes lack efficient, comprehensive methods for substantially reducing the oxygen demand of the wastes while also removing harmful chlorides and the like which cause corrosion of the waste processing equipment. Further, conventional processes do not adequately inhibit the formation or transfer of environmentally undesirable products. The present invention provides an integrated waste treatment system particularly suited for the processing of animal wastes which solves many of the problems associated with conventional waste processing systems.